Secondary batteries using a hydrogen rechargeable negative electrode are known. These batteries operate in a different manner than lead acid, nickel-cadmium or other battery systems. The rechargeable hydrogen storage electrochemical cell or battery utilizes a negative electrode that is capable of reversibly electrochemically storing hydrogen and usually employs a positive electrode of nickel hydroxide material. The negative and positive electrodes are spaced apart in an alkaline electrolyte. Upon application of an electrical current to the negative electrode, the negative electrode material (M) is charged by the absorption of hydrogen: EQU M+H.sub.2 O+e.sup.- .fwdarw.M-H+OH.sup.- (Charging) (1)
Upon discharge, the stored hydrogen is released to provide an electric current: EQU M-H+OH.sup.- .fwdarw.M+H.sub.2 O+e.sup.- (Discharging) (2)
The reactions are reversible, and this is also true of the reactions that take place at the positive electrode. As an example, the reactions at a conventional nickel hydroxide positive electrode as utilized in a hydrogen rechargeable secondary cell or battery are as follows: EQU Ni(OH).sub.2 +OH.sup.- .fwdarw.NiOOH+H.sub.2 O+e.sup.- (Charging) (3) EQU NiOOH+H.sub.2 O+e.sup.- .fwdarw.Ni(OH).sub.2 +OH.sup.- (Discharging) (4)
A battery utilizing an electrochemically hydrogen rechargeable negative electrode can offer important potential advantages over conventional secondary batteries. Hydrogen rechargeable negative electrodes should offer significantly higher specific charge capacities than lead or cadmium negative electrodes. Furthermore, lead acid batteries and nickel-cadmium type secondary batteries are relatively inefficient, because of their low storage capacity and cycle life. A higher energy density should be possible with hydrogen storage batteries than these conventional systems, making them particularly suitable for many commercial applications.
Suitable active materials for the negative electrode are disclosed in U.S. Pat. No. 4,551,400 to Sapru et al. These materials reversibly form hydrides in order to store hydrogen. Such materials have compositions of: EQU (TiV.sub.2-x Ni.sub.x).sub.1-y M.sub.y
where 0.2.ltoreq.x.ltoreq.1.0, 0.ltoreq.y.ltoreq.0.2 and M=Al or Zr;
Ti.sub.2-x Zr.sub.x V.sub.4-y Ni.sub.y
where, 0&lt;x.ltoreq.1.5, 0.6.ltoreq.y.ltoreq.3.5 and EQU Ti.sub.1-x Cr.sub.x V.sub.2-y Ni.sub.y
where, 0&lt;x.ltoreq.0.75, 0.2.ltoreq.y.ltoreq.1.0. Reference may be made to U.S. Pat. No. 4,551,400 for further descriptions of such materials and for methods of making them. Other suitable materials may also be used for the rechargeable hydrogen storage negative electrode.
The negative hydrogen storage electrode can be made by sintering particulate active material with a binder, such as nickel, that has been compressed. The compressed material is sintered in a suitable atmosphere, such as argon and hydrogen.
One problem that has been encountered in battery cells that use hydride materials as a negative rechargeable hydrogen storage electrode is that freshly made cells may not be able to deliver the expected high capacity even after multiple charge and discharge cycling of the sealed cells. In addition, even in cells that deliver the expected capacity, the pressure that develops during the charging cycle can be high and in some cases, can cause venting of the cell at an early stage.
A need exists for a hydrogen storage electrode and a sealed electrochemical hydrogen storage cell that efficiently utilizes the hydrogen storage capability of the hydrogen storage electrode.
A need also exists for a method of producing rechargeable negative hydrogen storage electrodes and for an improved electrode and cell that does not cause unacceptable or venting levels of pressure as a result of charging or overcharging when utilized in a sealed cell. An electrode having improved capacity and increased discharge rate would also be desirable.